The United States has no doubt that China's President Hu Jintao is in control of his country's military, U.S. Defense Secretary Robert Gates said on Friday.

Gates was speaking to university students in Tokyo just days after meetings in China meant to bolster ties with its military.

Gates expressed renewed concerns about a buildup by the People's Liberation Army, which flexed its muscle this week with its first-ever test flight of a stealth fighter jet, and called China's military modernisation programme opaque.